Catalyst system for converting emissions of a lean-burn engine
A catalyst system for attaining high conversions of NO, HC, and CO in a
fuel-lean emission flow (i.e., containing SO.sub.2, H.sub.2 O, H.sub.2,
and considerable excess oxygen), the system comprising: (a) a first stage
reducing catalyst for treating the nitric oxide emissions, the catalyst
containing highly acidic gamma alumina (i.e., with a pH.sub.pzc of less
than 3); (b) means for injecting gaseous or liquid reductants into the
emission stream prior to entering said first stage catalyst, said first
stage catalyst temperature being selected to be in the range of
550.degree.-650.degree. C.; and (c) an oxidation catalyst effective for
treating the effluent from the first stage catalyst.
Another aspect of this invention is a method of treating the exhaust gas
from a fuel-lean emission flow from a fossil-fueled internal combustion
engine having a redox ratio of 0.02-0.09, the method comprising: (a)
injecting a gaseous or liquid HC or oxygenated HC reductant into the
emission stream at a location where the stream is within the temperature
range of 550.degree.-650.degree. C.; (b) immediately exposing the injected
stream to a first stage catalyst containing acidic gamma alumina with a
Ph.sub.pzc of less than 3; and (c) exposing the effluent from the first
stage catalyst to an oxidation catalyst that is effective in ensuring that
the NO, HC, and CO in the emissions are each converted to at least 80%.
Subramanian; Somasundaram (Melvindale, MI), Kudla; Robert J. (Warren, MI), Chattha; Mohinder S. (Northville, MI) |
Ford Global Technologies, Inc.
July 23, 1992|